DESCRIPTION (Adapted from applicant's description): The long-term goal of this research is to investigate the following hypothesis: Soluble HLA-G derived from placentas has a profound influence on maternal and fetal immunity that benefits semiallogeneic pregnancy. To explore this postulate experimentally, the investigator plans to develop new tools and key preliminary data. Specific Aims are: 1) To prepare and characterize molecular probes and antibodies for identification of specific HLA-G transcripts and proteins; 2) To: a) develop an in vitro mammalian expression system to produce soluble HLA-G; (b) use the soluble HLA-G to establish an ELISA assay; and c) use the ELISA assay to test sera from nonpregnant and pregnant women for soluble HLA-G; and 3) To determine whether or not the placenta is a source of soluble HLA-G by ascertaining transcript and protein production patterns in specific cell lineages in first trimester and term placentas using in situ hybridization and immunohistology.